1. Field of the Invention
One disclosed aspect of the embodiments relates to solid-state image pickup elements, distance detecting apparatuses including the solid-state image pickup element, and cameras including the distance detecting apparatus, and it particularly relates to a solid-state image pickup element for distance detection such as a digital still camera or digital video camera.
2. Description of the Related Art
A solid-state image pickup element has been proposed (Japanese Patent No. 4027113) which detects a distance by a phase difference detection method with distance detection pixels having a distance detection (focal point detection) function as a part or all of pixels of the solid-state image pickup element in a digital still camera or a video camera, for example. Each of the distance detection pixels here has a plurality of photoelectric conversion units. A light flux having passed through different areas of an exit pupil of an imaging lens is guided to different photoelectric conversion units. The plurality of thus configured distance detection pixels are used to detect images (Image A, Image B), formed by light fluxes having passed through different areas of the exit pupil and measure the amount of displacement between Image A and Image B. The amount of defocus is calculated from the amount of displacement and a base length (an interval between different areas of the exit pupil) to detect the distance (focal point position).
However, in a solid-state image pickup element according to the conventional example, since distance detection pixels have a plurality of photoelectric conversion units require a plurality of signal detecting circuits for reading signals from the photoelectric conversion units. The plurality of signal detecting circuit may lower the aperture ratio of the photoelectric conversion units (the ratio of the photoelectric conversion units occupying the pixels) and prevent efficient reception of light from a subject at all times. As a result, the SN ratio of the ranging signal may be deteriorated, and the number of distance detection errors may increase.